Rochelle salt piezoelectric crystal apparatus



Dec. 1, 1942. w. P. MASON 2,393,375

ROCHELLE SALT PIEZOELEC TRIC CRYSTAL APPARATUS Filed June 10, 1941 3Sheets-Sheet 1 /NVEN7'0R W R MASON A TTORNE V Dec. 1, 1942. w p MASON2,303,375

ROCHELLE SALT PIEZOELECTRIC CRYS TAL APPARATUS Filed June 10, 1941 3Sheets-Sheet 2 FIG. 7 FIG. 8

7 /0\ I /o ,4 /2 [7 v/s T F IG. .9

/0 II l2 I! I4 I5 I617 I6 I9 202/ 22 28242528 272! 2980 RATIO, X AXISLENGTH L DIMENSION T0 Y AXIS THICKNESS 7' DIMENSION lNl/ENTOR W P. MASONA TTORNE) 1942- w. P. MASON 2,303,375

ROCHELLE SALT PIEZOELECTRIC CRYSTAL APPARATUS Filed June 10, 1941 3Sheets-Sheet 3 FIG. I0

I Z 1.120 L ous" SECOND SHEAR MODE IJIO X SHEAR M005 FREQUENCY IIVKILOCYCLES PER SECOND PER MILL/METER 0F THICKNESS T 1o 11 12 1.1 14 '151a 17 1a .19 2a 21 22 2a 24 2s 2s 27 2a 29 30 T10 r 4x1: 1:11am I.DIMENSION 70 7111001255 1 mums/01v RATIO Z AXIS LENGTH L DIMENSION T0THICKNESS T DIMENSION mum/r01? W P MASON A TTORNEY' Patented Dec. 1,1942 ROCHELLE SALT PIEZOELECTRIC QRYSTAL APPARATUS Warren P. Mason, WestOrange, N. J., assignor to Bell Telephone Laboratories, Incorporated,New York, N. Y., a corporation of New York Application june 10, 1941,Serial No. 397,377

14 Claims. (01. 171-327) This invention relates to piezoelectric crystalapparatus and particularly to high frequency piezoelectric Rochelle saltor sodium potassium tartrate crystal elements suitable for use as cir-'cuit elements in electric wave filter systems and oscillator systems,for example.

One of the objects of this invention is to provide a Rochelle saltpiezoelectric crystal element having one or more useful high frequencyor thickness modes of motion that may be utilized alone orsimultaneously without interference with other modes of motion therein.

Another object of this invention is to provide a Rochelle salt crystalelement having a plurality of simultaneously useful and independentlycontrolled thickness mode frequencies.

Another object of this invention is to provide Rochelle salt crystalelements utilizing either the first shear thickness mode of motionthereof or the second shear thickness mode of motion thereof.

Another object of this invention is to reduce the number and the costof. crystals used in high frequency electric wave filter systems andother wave transmission networks, and 'to take advantage of the highpiezoelectric activity and low cost of Rochelle salt.

Rochelle salt piezoelectric crystal elements generally may be excited inmany different modes of motion such as extensional or longitudinal modesof motion, fiexural modes of motion, and shear modes of motion, forexample. When crystals are to be applied to filter systems, for example,it is generally desirable to have all of the undesired or extraneousmodes of motion therein uncoupled with and considerably higher, or lowerin frequency than the desired main mode or modes of motion of thecrystal element since otherwise the extraneous resonance frequenciestherein may introduce undesirable frequencies or pass bands in thefilter characteristics. Accordingly, it is often desirable in filtersystems and elsewhere that the desired main mode or modes of motion-of acrystal element be substantially independent of other modes of motionand independently controlled in order that such desired mode or modes ofmotion-may be given any desired frequencyyalues to obtain prescribedfrequency characteristics.

In accordance with this invention, wave filters and other systems maycomprise as a component provide either separately or simultaneouslyuseful effective resonances which may be independently controlledandplaced-at predetermined frequencies of nearly the same value or ofdifierent values, for use in an electric wavefilter, or elsewhere. 1 Y

The crystal element may be a Rochelle salt a type crystal plate ofsuitabl orientation with respect to the X, Y and Z axes thereof, and ofsuitable dimensional proportions, and provided with a suitable electrodearrangement and connections for separately driving either orsimultaneously driving both of two thickness modes of motion therein,and independently controlling the relative strengths of such resonances.

In particular embodiments, the orientation of the Rochelle salt crystalelement may be such element thereof, a single piezoelectric crystalelement of Rochelle salt which maybe adapted to vibrate simultaneously.in a plurality of high frequency or thickness modes of motion in orderto that one of the major surface dimensions thereof, such as the lengthdimension, lies along one of the X, Y and Z axes thereof, and the otherdimension, such as the width dimension of the.

major surfaces, is rotated in eflect a selected angle in degrees to aposition intermediate or midway between the other two of the X, Y and Zaxes. The major surfaces may be of rectangular or square shape. Thefrequency-determining thickness dimension between the major surfaces ofthe crystal element and the length dimension thereof may be'made ofselected and related values, as a dimensional ratio of the lengthdimension with respect ,to the thickness dimension in the region from 10to 50, in order -to obtain therefrom, separately or simultaneously,either or both of two useful independently controlled resonantfrequencies resulting from two independently controlled thickness modesof motion, one particular set of which is described herein as thefundamental or first shear thickness mode of 'motion and the other asthe second shear thickness mode of motion. Both the first and secondshear mode frequencies are controlled mainly by the thickness dimensionof the'crystal element andvary inversely as the value of the thicknessdimension of the crystal element.

The Rochelle salt crystal elements described herein may have the same orsimilar orientations as those described in my United States Patent2,178,146, dated October 31, 1939, but herein they are adapted for aplurality of thickness mode ,vibrations of the shear type including thefirst shear and also the second shear modes of motion. 4 Such Rochellesalt crystal'elements when provided with suitable electrodes may beconnected into a filter circuit'in sucha way that one of the resonancesof each crystal element is effective asosevs n. the line branch anotherof such resonances agonal branch of the lattice of the elect networkthereof, in to obtain filter circuits using a single other crystal whichare electrically equivalent to circuits requiring two crystals, therebyreducing the and cost numb er Rochelle example stiuctu' of crystalstherein. Such elements may be utilized for on my application er ll),15339, one. in

1, o granted Marc 3i, on application Tole. seas-es, filed December i)1on9 no- By using two oi su salt crystal elements systems rat .e isinez-ipensively cons several million igher values of in the passtemperature he higher values filters us'sg the vibrat o ob'aincha'l'acteris obtained when usin cycles per control c te havetemperature ntigi de to hold th 'equency.

o ory Rochelle 1 .def 1113613 or for without change in the a long periodof characteristics ther For a clearer not 1 this ention and theadditional advantages, feat :es and objects t reference made enconnection gs, in which like like or similar with the accompan referencecharacters represent parts and in which: I

l, 2 and 3 are perspective views of three forms of piezoelectric Rohelle salt crystal elements in accordance with this invention, andrespwtively illustrate particularly the orientation thereof with respectto the and Z axes of the nding of the nature of Rochelle salt crystalmaterial from which the 7 crystal elements be cut:

Figs. l to 8 are views illustrating types of electrodes and connectionswhich may be utilized with any of the Rochelle salt crystal elements ofFig. l, 2 or 3 to drive the crystal element sepa rately in either, orsimultaneously in both, of two independent shear thickness modes ofmotion, in order to obtain the desired resonance frequency Orfrequencies;

Fig. 4 is a perspective view of an electrode arrangement that may beused to driveany or the piezoelectric crystal elements of Fig. 1, 2 or 3in the fundamental or first shear thickness mode of motion; I

Figsj5 and 6 are perspective views of electrode arrangements that may beused to drive any of the crystal elements of Fig. 1, 2 or '3 in thesecond shear thickness mode of motion and the fundamental or first shearthickness mode of motion, separately or simultaneously;

Fig. '7 is a schematic diagram illustrating an example of balancedfilter connections that may be used with the crystal element electrodesoi Fig. 8 is a schematic diagram illustrating an example of unbalanced nor connections that may be used with the electrodes of the crystalelement of Fig. 6;

9 is a graph illustrating the thickness mode frequency-dimensionconstants of the fundamental or first shear mode of motion and of thesecond shear mode of motion in the Rochelle salt crystal elementillustrated in Fig. 1 having a dimensional ratio of its X axis length Lwith respect to its thickness '1 in the region from 12 to 30.

Figs. 10 and 11 are graphs illustrating the thickness-mode i*equency-dimcnsion constants of the first and second shear modevibrations of the Rochelle salt crystal elements illustrated in Figs. 2and 3 respectively, for ratios of the length L with respect to thethickness T in the region from about 12 to 30.

This specification follows the conventional terminology as applied tocrystalline Rochelle salt, which employs three orthogonal. or mutuallyperpendicular h and c axes or X. Y and axes, respectively, as shown inthe drawings, to desigan electric axis, a mechanical axis and the opticaxis, respectively, of piezoelectric Rochelle salt or sodium potassiumtartrate crystal material, and which employs three orthogonal. axes X, Yand Z to designate the directions of axes of a piezoelectric bodysingularly oriented with respect to such X, Y and 23 axes thereof. Wherethe orientation is obtained in effect by a single rotation of theRochelle salt crystal element, the rotation being in effectsubstantially about the length dimension axis X, :7 or Z of thepiezoelectric body as illustrated in Figs. 1, 2 and 3, respectively, theorientation an les, respectively s=substantially degrees, 6:45 degrees,and

=45 degrees designate in degrees the effective angular position oi thewidth axis dimension W of the crystal plate as measured from one of theother two of the X, Y and Z axes. The relation of ie X, Y and Z axes tothe outer of a grown. Rochelle salt crystal body are illustrated in W.P. Mason United States Patent 2,178,146, dated October 31, 1939.Rochelle salt belongs to the rhombic hemihedral class of crystals andhas three orthogonal or mutually perpendicular axes generally designatedas the h, and c axes or the X, Y and Z axes, respectively.

Referring to the drawings, Figs. 1, represent perspective views of thinbare piezoelectric Rochelle salt crystal elements l, 2 and 3 out fromcrystalline Rochelle salt free from defects and made into a plate ofsubstantially rectangular parallelepiped shape with its major surfaceshaving a length dimension L, and a width dimension W which isperpendicular to and may be equal to or longer or shorter than thelength dimension L. The frequency-determining thickness or thindimension T between the major surfaces is perpendicular to the other twodimensions L and W. In accordance with the particular orientation andmode or modes of motion selected, the final width dimension W or lengthdimension L of the Rochelle salt crystal element I, 2 or 3 of Figs. 1, 2and 3 may be made of a, suitable value with respect to the thicknessdimension T according to the desired resonant frequency. The widthdimension W also may be equal to or otherwise related to the lengthdimension L to remove spurious frequencies from the region of thedesired resonant frequency. The thickness dimension T may be of theorder 2 and 3 of 1 millimeter more or less and made ofany suitablevalueto obtain the desired thickness mode frequency or frequencies for thecrystal element I, 2 or 3 of Figs. 1, 2 and 3.

As shown in Fig. 1, the length dimension L of the Rochelle salt crystalelementgl illustrated in Fig. 1 lies substantially along or parallel tothe X axis, the X axis being perpendicular to the plane of themechanical axis Y and the optic axis Z of the Rochelle salt crystalmaterial from which the element I is cut. The width dimension W which isperpendicular to the length dimension L, is inclined at an angle of adegrees with respect to said Z axis, the angle a being one of the valuesinthe region of substantially 45 degrees (45). The major surfaces andthe major plane of the Rochelle salt crystal element I are disposedparallel or nearly parallel with respect to the X axis, the lengthdimension L and the width dimension W lying along the X axis and the Zaxis, respectively, the Z axis being inclined at the angle a withrespect to the optic axis Z. The axis Z is accordingly the result of asingle rotation of the width dimension W about the X axis degrees. Itwill be noted that the crystal element I of Fig. l is in effect a Y-cutRochelle salt crystal plate rotated at degrees about the X axis.

Fig. 2 is a perspective view of a Rochelle salt piezoelectric crystalelement 2 having its length dimension L along or parallel to the Y axisand its width dimension W inclined at an angle of 0=substantially 45degrees with respect to the Z axis, the major surfaces of the crystalelement 2 being parallel or nearly parallel to the Y axis.

Fig. 3 represents a Rochelle salt crystal element 3 having its lengthdimension L along or parallel to the Z axis and its width dimension Winclined at an angle which may be any angle in the region of'45 degreesintermediate the X and -Y axes, the major surfaces of the crystalelement 3 being parallel or nearly parallel to the Z axis.

The orientations illustrated in Figs. 1, 2 and 3 represent Rochelle saltpiezoelectric crystal ele-, ments I, 2 and 3, respectively, which may beadapted for a plurality of independently controlled thickness modevibrations of the shear motion type, which may be utilized either aloneor simultaneously, according to the arrangement of the electrodes andconnections that are used therewith, and the dimension-frequencyconstants that are selected therefor.

Suitable conductive electrodes, such as the crystal electrodes of Fig.4, 5 or 6, for example,v may be placed on or adjacent to or formedintegral with the opposite major surfaces of the crystal plate I, 2 or 3of Fig. 1, 2 or 3 in order illustrated in Fig. 1, or 0==substantiallydegrees with respect to the Z axis as illustrated in Fig. 2, or=substantially 45 degrees with respect to the Y axis, asillustrated inFig. 3, the thickness T shear mode vibrations comprising the first shearmode of motion and the second shear mode of motion in the crystal platemay be used simultaneously,

To obtain the two thickness shear type modes of motion simultaneously,it is necessary that the crystal element have apiezoelectric' constantwhich will generate a first shear motion along the thickness dimension Tand also a piezoelectric constant that will generate a second shearmotion along the thicknessdimension T.

In the case of the Rochelle salt crystal element I illustrated in Fig.l, the requirement of suitable piezoelectric constants may be met whenthe width dimension W or the length dimension L is inclined at anysuitable angle win the region to apply electric field excitation to theRochelle salt plate. I, 2 or 3 which may be vibrated alone orsimultaneously in the desired thickness T fundamental or first shearmode of motion and/or the thickness T second shear mode of motion atindependently controlled resonant response. frequencies which dependupon dimensions involving the thickness dimension T and i also the widthdimension W or the length dimension L, the fundamental shear thicknessmode frequencies for the three cuts of Figs. 1,- 2 and 3 being valuesroughly ranging from about 940 to 1272 kilocycles per second'permillimeter of the thickness dimension T and varying inversely as thevalue of the thickness dimension T.

of 45 degrees between the Y and Z axes of the YZ plane, the X axis beingparallel or nearly parallel to the major planeand the major surfaces ofthe Rochelle salt crystal element i of Fig. 1. Reference is made to mypaper A dynamic measurement of the elastic, electric and piezoelectricconstants of Rochelle salt published April 15, 1939, in Physical Review,volume 55, page 775, for information on the piezoelectric constantsinvolved in shear mode vibrations along the thickness dimension T ofRochelle'salt crystal elements. The shear mode piezoelectric constantsreach their maximum values when the angle 11:45 degrees or when theplane formed by the width dimension W and the length dimen sion L of theRochelle salt crystal element I of Fig. l is inclined at an angle of 45degrees with respect to the Y and Z axes thereof, the major plane andmajor surfaces thereof being perpendicular or nearly perpendicular tothe plane of such Y and Z axes.

While the maximum values of the thickness shear mode piezoelectricconstants occur when the angle =45, the angles of a in the region of 45degrees are near enough thereto obtain good values of piezoelectricconstants for the first and second shear thickness modes of motion. SuchRochelle salt crystal elements I of- Fig. 1 havean electromechanicalcoupling which varies with temperature change, and are easily driven by"45 degrees with respect to the Z axis and the X axis also may be used asa doubly resonant crystal element. Such an element has anelectromechanical coupling that does not vary much in "fig. o e n nearlyparallel to the e-Xis also may l e used to g a nerate thickness modefirt J vibrations of the k nd useful for a crystal e'len n' then the ssoon *he lie 1 o. near mo uaviug the orienor 3 "may conto r b.0113illustrated oiled by the value or t dii "nd the dimension ng 't' th re111i d sion co ouencies ely the second sheer indanientai or first motioc with respect to the vmclrness dimer sion T is in a region and in thisregion the resonances of these two modes are substantially uncoupled.sir-only very loosely coupled.

Accordingly, when the dimensional ratio of the length L and the width Wwith respect to the thickness T is in the proper region, and the crystalorientation is that of Fig. l, 2 or 3, the frequencies of these twoindependent modes of vibration may be placed close together butsufliciently uncoupled or separated to provide simultaneously twoindependently controlled frequencies from the same Rochelle salt crystalelement, which may be usefully employed in a filter system I mentalshear thic for example, to give conveniently two useful frewhen used c.A

v 2 and 3 respectively asoasrsing substantially square major surface: isgiven by the experimentally determined relation:

7 ow -r1) n where L is the value or? the X axis length dimension and Tis the value of the thickness dimension of the crystal element l of Fig.1 expressed in millimeters.

The second shear expressed in iilliJCyC l' crystal plate l of .L.square. major surfaces i mentally determined relation:

end

; iii."

e rreduency of 1e cry any number of in frequen 3. than oi hiclrness modefrequency, and er stern, one resonance fro i one arm, and the other,ency the other so that a we attenuation peaks can he made from onecrystal. Similarly, the first shear and the second shear thickness anodequencies of the crys elements 2 and 3 may be utilized.

The grenh oi. illustrates the measured resonanc Ireouencies associatedwith the funda mental or first shear thickness mode oi ion (curve A) andalso those associated with. the t end shear thickness node of motion(curve 33'), in a Rochelle c1 tal element cving square or nearly squaremajor surfaces orientation angl of suostantially as degrees as illustrated i. g. 1. In Figv the funds.

ess mode i esented by the gen lly horizo .l. wardly sloping curve A andhas e. frequenc dimension constant of 94C to Q50 lrilocycles per secondper millimeter of thickness dimen sion 1'' which is dependent but littleupon the dimensional ratio of the X axis length L with respect to the Yaxis thickness T. The second overtone shear thickness mode frequency isrepresented by the downwardly sloping inclined curve B and has afrequency-dimension constant from about 945 to 990 kilocycles per secondper millimeter of thickness dimension T dependent upon the value of theselected dimensional ratio of the X axis length dimension L with respectto the thickness dimension T within the dimensional ratio range fromabout 12 to 30, the frequency constant values gradually decreasing withincreasing values for the dimensional ratio. As shown by the curves Aand B of Fig. 9, the freselected the IZZY fir quency' in resonance freoquency of the second shear mode of motion and by the curves of Figs. and11, similar in form' to the downwardly sloping first and second shearmode curves A and B of Fig. 9 for. the crystal element l of Fig. 1 butare somewhat higher in frequency thanthe first and second shear modefrequencies of the crystal element I of Figs. 1 and 9 for a givendimensional ratio of the length L or the width W with respect to thethickness T.

The thickness mode frequency-dimension constants for thedsecond shearthickness mode of motion in the Rochelle salt crystal element 2 of Fig.2are roughly from 1277 to 1330 kilocycles per second per millimeter ofthe thickness dimension T within a range of dimensional ratios of thelength L and width W with respect to the thickness T from about 12 to30, the frequency constant values gradually decreasing with increasingvalues for the dimensional ratio as illustrated by the downwardlysloping curve B of Fig. 10; and the frequency-dimension constants forthe second shear thickness mode of motion in the Rochelle salt crystalelement 3 of Fig. 3 are, as illustrated .by theclownwardly sloping curveB" of Fig. 11, roughly from 1060 to 1107 kilocycles per second permillimeter of the thickness dimension T within a range of dimensionalratios of the length L and width W with respect to the thickness T fromabout 12 to 30, the corresponding curves for such second shear modefrequencies of the crystal element 2 of Fig. 2 and for the crystalelement 3 of Fig. 3 being similar in form as hereinbefore stated to thedownwardly sloping second shear modecurve B of Fig. 9 but somewhathigher in frequency, for a given dimensional ratio, the frequencyconstant values gradually decreasing with increasing values for thedimensional ratio in accord ance with the form of the downwardly slopingcurve B of Fig. 9.

The thickness mode frequency-dimension constants for the fundamental orfirst shear mode of motion are somewhat lower than those given above forthe second shear mode of motion; and as illustrated by the curves A, Aand A" 9, 10 and 11 for the Rochelle salt crystal elements l, 2 and 3 ofFigs. 1, 2 and 3 are respectively, expressed in kilocycles per second,about from 942.5 to 948, from 1265 to 1272 and from 1052 to 1060,respectively, for dimensional ratios of the length L and width W withrespect to the thickness T in the range about from 12 to 30, thefrequency constant values gradually decreasing with increasing valuesfor the dimensional ratio in accordance with the form of the slightlydownwardly sloping curve B of Fig. 9.

Accordingly, it will be understood that the curves for the first andsecond shear mode frequencies givenin Fig. 9 for the crystal element 1of Fig. 1 also apply to the crystal elements 2 and 3 of Figs. 2 and 3using the same length to thickness dimensional ratio values of Fig. 9but changing the ordinate values thereof to correspond with the limitingranges of the frequency constant such shear thickness mode resonancefrequencies of a desired value.

In Fig. 4 which is a perspective view of the Rochelle salt crystalelement of Fig. 1, 2 or 3, the pair of opposite electrodes 9 and I5 maybe utilized to usefully operate separately in the crystal element I, 2or 3 of Figs. 1 to 3, the fundamental or any odd order harmonicthickness shear mode of motion, the fundamental frequency being roughlyone of the values from about 942 to 1272 kilocycles per second permillimeter of thickness dimension T, dependent upon the orientationselected. The electrodes 9 and I5 may partially or wholly cover themajor surfaces of the crystal element I, 2 or 3 and may be connected incircuit by a conductive member disposed in contact with each of theelectrodes 9 and I5 at or near the corners thereof. It will beunderstood that Rochelle salt crystal elements having the orientationsillustrated in Figs. 1, 2 and 3 and provided with electrodes of the typeillustrated in Fig. 4 may be utilized to obtain a desired fundamental orodd order harmonic shear mode vibrational frequency that is dependentsubstantially upon the thickness dimension T. Where a harmonic of suchfundamental shear mode of motion is used, the harmonic frequency may bevalues hereinbefore given for such frequencies. I

Figs. 4, 5 and 6 illustrate forms'of electrode arrangements which may beutilized to drive any of the crystal elements of Fig. 1, 2 or 3. In Fig.4, the single pair of electrodes 9 and I 5 may be used to drive eitherthe thickness T shear fundamental mode of motion or any odd harmonicsuch as third, fifth, etc., harmonic thereof to obtainseparately but notsimultaneously any of -of any desired odd order and may be obtained bythe use of electrode-arrangement shown in Fig. 4.

As shown in Fig. 5, the second shear thickness mode of motion may bedriven by means of two pairs of divided electrodes H), II, l2 and I3placed on both of the major surfaces of the crystal element of Fig. 1, 2or 3; and with suit able connections, the fundamental or first shearmode of motion may be driven at the same time by one of the connectedsets of electrode platings, with the result that the two usefulandindependently controlled thickness mode resonance frequencies of thecrystal element L2 'or 3 may be made to appear simultaneously. Asillustrated in Fig. 5, the Rochelle salt crystal element I, 2 or 3 ofFig. 1, 2 or 3 may be provided with four equal area electrodes I 0, ll,l2 and I3, two

of the electrodes l0 and H being placed on one major surface of thecrystal element with a centrally located narrow transverse split or gap1 therebetween, and the other two electrodes l2 and I3, being oppositelydisposed and placed on the opposite major surface of the crystal elementand separated with a similar narrow and oppositely disposed split ordividing line 1 therebetween, the dividing lines 1 extending generallyin the direction of the width W axis of the crystal element, accordingto the value of the angle selected between the direction of the dividingline I and the direction of the length. dimension L. The gap orseparation 1 between the electrode coatings or platings on each of themajor surfaces of the crystal element may be of the order of about 0.3millimeter, the center line of such splits in the platings on theopposite sides of the crystal plate I being aligned with respect to eachother.

When the electrode plates have the same sign across the Whole surface ofthe major surface, the fundamental thickness shear vibration of thecrystal element is excited; and when the electrode plates have oppositesigns on'the same major surface of the crystal element, the secondthickness shear mode vibration, corresponding to the fundamental shearmode for a crystal plate half as long as the length L of the originalcrystal element, is excited, the second shear orancii oi the equivalentlate diagonal branch there- *ully in connection with i and 3application, Serial ,lli'? referred to hereinceiore. oe balanced circuitof Fig. 5' may be con" ted into an unbalanced filter structure byinectirlg the t o electrodes '3? and on no major 5 aces of the crystalelement. his case, the two electrodes and of Figs. nay be replaced by asingle electrode i5 ay be connected. as shown 8 and as described more nwith Figs. 6 and '7 of the Serial No. 303,757 hereinbefully in. comicMason applies. lore referred to.

As illustrated in Fig. 8 to reduce the magnitude of the shuntingcapacitance appearing in the line branch of the lattice portion, anarrow grounding strip i i of metallic or conductive coating or platingmay be placed on one major surface of the crystal element between theelectrodes if and The strip l4 may extend around one edge of the crystalelement to the opposite major suriace thereof where it may be.

electrically connected to the large electrode IS. The ground strip ismay be approximately 1 millimeter in width and may be placed between andseparated from the two electrodes Ill and H on the same major surface ofthe crystal element 1, in order to provide shielding and to reduce straycapacities to a minimum. The strip of plating 14 may extend from onemajor surface continuously over and around one edge only or both edgesof the crystal plate I to the opposite major face thereof where it maymake contact with the integral electrode 15 on that surface.

It will be noted that in order to drive the electroded crystal elementof Fig. 6 in the second shear thickness mode of motion, one-half ofthecrystal plate I is made of opposite polarity to that of the other half,as indicated by the and signs in Fig. 6, and that this may beaccomplished by utilizing a crystal element having divided metalliccoatings l0 and l!.placed on one of its major surfaces and connected inthe form of a T network, for example, as illustrated in Fig. 8.Inductance coils may be added in the usual manner in series or inparallel with the network of Fig. 8 to produce broad band low or highimpedance filters for example. In order that the crystal impedance mayappear in both arms of the lattice structure of Fig. 8, one mode isdriven when the terminals 2| and 23 are both of same polarity, and theother mode is driven when these terminals 2| and 23 are of oppositepolarity. Since both modes are substantially uncoupled or independent,they may produce simultaneously two independently controlled resonancesof predetermined frequencies of desired values.

ce uencies, one of which may and the electroded crystal in order tocontrol the relative impedance levels of the two desired. crystalresonances, the crystal electrodes associated with one half of the majorsuriace or surfaces of crystal element l, 2 or 3 of Figs. 5 and 6 may beextended to cover a portion of the other half thereof. This may be done,for example, by adjustment of the position of the electrode dividingline angle with respect to the length dimension L. The angle may be anydesired value over a wide range of angles. This adjustment does notmaterially affect the impedance of the first shear mode resonance, butwith decreasing values for the SO-degree' angle shown in Figs. 5 and 6,will increase the im pedance level and cut down the drive on secondshear mode resonance, without materially affooting the impedance of thefirst shear modc resonance. Thus, by changing the angle of inclinationof the split or division line I between the electrodes and i l withrespect to the length dimension L of the crystal element, illustrated bythe QO-degree angle in Figs. 5 and 6, the internalcepacity associatedwith the second shear mode resonance, which is nearly a maximum valuewhen the angle equals degrees as shown in Figs. and 6, may be varied andadjusted to a desired value without changing the internal capacityassociated with the first shear mode resonance.

It will be understood that the circuit illustrated in Figs. 7 and 8represent particular circuits. These and other forms of filter circuits,which doubly resonant crystal element may be utilized, are described inW. P. Mason application Serial No. 303,757, hereinbefore referred to. Ifdesired, mutual inductance may be used between the end coils of thecrystal filter to obtain improved attenuation characteristics asdescribed in United States Patent No. 2,198,684, granted April 30, 1940,to R. A. Sykes.

The electrode doubly resonant crystal elements of Figs. 4, 5 and 6 maybe mounted in any suitable manner, such as by clamping or otherwise.Where the clamping form of mounting is used, one or more pairs such asfour pairs of opposite conductive clamping projections may resilientlycontact the electroded crystal element at or near its four corners onlyin order to support and to establish individual electrical connectionstherewith.

Alternatively, instead of being mounted by clamping, the electrodedcrystal plate may be mounted and electrically connected by cementing orotherwise firmly attaching fine conductive supporting wires directly toa thickened part of the electrodes of the crystal element at or near itsfour corners only. Such fine supporting wires secured to the electrodcdcrystal element may extend horizontally from the vertical disposed majorsurfaces of the crystal element, and at their other ends be attached bysolder, for example, to vertical conductive wires or rods carried by thepress or other part of an evacuated or sealed glass or metal tube. Thesupporting wires and rods may have one or more bends therein toresiliently absorb mechanical vibrations. Also, bumpers or stops of softresilient material such as mica may be spaced closely adjacent theedges, ends or other parts of the electroded crystal element in order tolimit the bodily displacement thereof when the device is subjected tomechanical shock. Fig. 8, for example, of A. W. Ziegler United StatesPatent 2,275,122, granted March 3, 1942, on application Serial No.338,871, filed June 5, 1940, illustrates a suitable mounting of thistype for the crystal element, the horizontal supporting wires beingspaced along the vertical rods to suit the comer spacing of theelectroded crystal element. It will be understood that any holder whichwill give stability, substantial freedom from spurious frequencies anda, relatively high Q or reactance-resistance ratio for the crystalelement may be utilized for mounting the crystal element.

Although this invention had been described and illustrated in relationto specific arrangements, it is to be understood that it is capable ofapplication in other organizations and is, therefore, not to be limited"to the particular embodiments disclosed, but only by the scope of theappended claims and the state of the prior art.

What is claimed is:

1. A high frequencysecond shear thickness mode piezoelectric Rochellesalt type crystal ele-' ment having its substantially square majorsurfaces substantially parallel to an X axis, said major surfaces beinginclined at an angle of substantially 45 degrees with respect to the Zaxis and the Y axis, the dimensional ratio of said X axis dimension ofsaid major surfaces with respect to the thickness dimension between saidmajor surfaces being one of the values between substantially 12 and 30,said thickness dimension .expressed in millimeters being one of thevalues between substantially 948 and 990 divided by the value of saidfrequency expressed in kilocycles per second.

2. A high frequency second shear thickness mode piezoelectric Rochellesalt type crystal element having its substantially square major surfacessubstantially parallel to a Y axis, said major surfaces being inclinedat an angle of substantially 45 degrees with respect to the Z axis andthe X axis, the dimensional ratio of said Y axis dimension of said majorsurfaces with respect to the thickness dimension between said majorsurfaces being one of the values between substantially l2 and 30, saidthickness dimension expressed in millimeters being one of the valuessubstantially from 1277 to 1330 divided by the value of said frequencyexpressed in kilocycles per second.

3. A high frequency second shear thickness mode piezoelectric Rochellesalt type crystal element having its substantially square major surfacessubstantially parallel to a Z axis, said major surfaces being inclinedat an angle of substantially 45 degrees with respect tothe Y axis andthe X axis, the dimensional ratio'of said Z axis dimension of said majorsurfaces with respect to the thickness dimension between said majorsurfaces being one of the values between substantially 12 and 30, saidthickness dimension expressed in millimeters being one of the valuessubstantially from 1060 t 1107 divided by the value of said frequencyexpressed in kilocycles per second.

4. A piezoelectric Rochelle salt type crystal element having itssubstantially rectangular major surfaces substantially parallel to oneof the three mutually perpendicular X, Y and Z axes thereof, 'said majorsurfaces being inclined at an angle intermediate the other two of saidthree X, Y and Z axes, the dimensional ratio of the dimension of saidmajor surfaces along said one of said X, Y and Z axes with respect tothe thickness dimension between said major surfaces being one of thevalues between substantially 12 and 30, and means including a pluralityof sets of functionally independent electrodes adjacent [said majorsurfaces for operating said element simultaneously at a plurality ofindependently controlled frequencies dependent upon said dimensions, oneof said frequencies being dependent upon the second shear thickness modevibration. 1

5. A piezoelectric Rochelle salt type crystal element having itssubstantially rectangular major surfaces substantially parallel to oneof the three mutually perpendicular X, Y and Z axes thereof, said majorsurfacesv being inclined at an angle of substantially 45 degrees withrespect to the other two of said three X, Y and Z axes, the dimensionalratioof the dimension of said major surfaces along said one of said X, Yand Z axes with respect to the thickness dimension between said majorsurfaces being one of the values substantially in the region of from 10to 5b, and

means including a plurality of sets of functionally independentelectrodes adjacent said major surfaces for operating said elementsimultaneously at a plurality of independently controlled frequenciesdependent upon said dimensions, one of said frequencies being dependentupon the fundamental or first shear mode vibration along said thicknessdimension, and another of said frequencies being dependent upon thesecond shear mode vibration along said thickness dimension.

6. A piezoelectric Rochelle salt type crystal I element adapted tovibrate simultaneously at desired independently controlled first andsecond shear thickness mode frequencies dependent mainly upon the lengthdimension of and the thickness dimension between its substantiallyrectangular major surfaces, said length dimension being substantiallyparallel to an X axis, said major surfaces being inclined at an angle'of substantially 45,degrees with respect to the Z axis, the ratio ofsaid length dimension of said major surfaces with respect to saidthickness dimension being one of the values within the region fromsubstantially l2'to 30, said thickness dimension expressed inmillimeters being one of the values from about 948 to 990v divided bythe value of said second shear mode frequency expressed in kilocycleslper second.

'7. A piezoelectric Rochelle salt type crystal element adapted tovibrate simultaneously at desired independently controlled first andsecond shear thickness mode frequencies dependent mainly upon the lengthdimension of and the .thickness dimensionv between its substantiallyrectangular major surfaces, said length dimension being substantiallyparallel to a Y axis, said major surfaces being inclined at an angle ofsubstantially 45 degrees with respect to the Z axis, the ratio of said Yaxis length dimension of said major surfaces with respect to saidthickness dimension being one of the values within the regionsubstantially from 12 to 30, said thickness dimension expressed inmillimeters being one of the values substantially from 1277 to 1330divided by the value of said second shear mode frequency expressed inkilocycles per second.

8. A piezoelectric Rochelle salt type crystal element adapted to vibratesimultaneously at desired independently controlled first and secondshear thickness mode frequencies dependent mainly upon the lengthdimension of and the thickness dimension between its substantiallyrectangular major surfaces, said length dimension being substantiallyparallel to a Z axis, said major surfaces being inclined at an angle ofsubstantially 45 degrees with respect to the if axis, the ratio of saidaxis length dimension of said major surfaces with respect to said.thickness dimension being one of the values within the regionsubstantially from 12 to 30, said thickness dimension expressed inmillimeters being one of the values substantially from 1060 to ill)?divided by the value of said second shear mode frequency expressed inkilocycles per second.

9. A piezoelectric Rochelle salt type crystal element adapted to vibratesimultaneously at independently controlled first and second shearthickness mode frequencies dependent mainly upon its length andthickness dimensions, said length dimension of the major surfaces beingsubstantially parallel to an X axis, said major surfaces being inclinedat an angle of substantially 45 degrees with respect to the Z axis, saidmajor surfaces being substantially square, the ratio of said X axislength dimension of said major surfaces with respect to said thicknessdimension being one of the values within the range from substantially 12to 30, said thickness dimension and said X axis length dimension being aset of corresponding values in accordance with the values of said firstshear and second shear frequencies.

10. A piezoelectric Rochelle salt type crystal element adapted --tovibrate simultaneously at desired independently controlled first andsecond shear thickness mode frequencies dependent mainly upon its lengthand thickness dimensions, said length dimension 'of the major surfacesbeing substantially parallel to a Y axis, said major surfaces beinginclined at an angle of substantially 45 degrees with respect to the Zaxis, said major surfaces being substantially square, the ratio of saidY axis length dimension of said major surfaces with respect to saidthickness dimension being one of the values within the range fromsubstantially 12 to 30, said thickness dimension and said Y axis lengthdimension being a set of corresponding values in accordance with thevalues of said first shear and second shear frequencies.

11. A piezoelectric'Rochelle salt type crystal element adapted tovibrate simultaneously at desired independently controlled first andsecond shear thickness mode frequencies dependent mainly upon its lengthand thickness dimensions,

said length dimension of the major surfaces being substantially parallelto a Z axis, said major surfaces being inclined at an angle ofsubstantially 45 degrees with respect to the Y axis, said major surfacesbeing substantially square, the ratio of said Z axis length dimension ofsaid major surfaces with respect to said thickness dimension being oneof the values within the range from substantially 12 to 30, saidthickness dimensionand said Z axis length dimension being a set ofcorresponding values in accordance with the values of said first shearand second shear frequencies.

12. A Rochelle salt type piez'oelectric crystal element adapted tovibrate at a desired second shear thickness mode frequency, said crystalelement having substantially rectangular shaped major surfaces, saidmajor surfaces having a.

asoaevt length dimension and a thickness or thin. dimensiontherebetween, said thickness dimension and said length dimension beingmade of values in accordance with the value of said desired second shearfrequency, said major surfaces and said length dimension beingsubstantially parallel to an X axis, said major surfaces being inclinedat an angle of substantially 45 degrees with respect to the Z axis, saidthickness dimension expressed in millimeters being one of the valuessubstantially from 948 to 990 divided by said desired frequencyexpressed in kilocycles per second, and the ratio of said X axis lengthdimension with respect to said thickness dimension being one of thevalues substantially from 30 to l2, said thickness dimension and saiddimensional ratio being corresponding values in accordance with thevalue of said frequency, as given by the curve B of Fig. 9.

13. A Rochelle salt type piezoelectric crystal element adapted tovibrate at a desired second shear thickness mode frequency, said crystalelement having substantially rectangular shaped major surfaces, saidmajor surfaces having a length dimension and a thickness or thindimension therebetween, said thickness dimension and said lengthdimension being made of values in accordance with the value of saiddesired second shear frequency, said major surfaces and said lengthdimension being substantially parallel to a Y axis, said major surfacesbeing inclined at an angle of substantially 45 degrees with respect tothe Z axis, said thickness dimension expressed in millimeters being oneof the values substantially from 1277 to 1330 divided by said desiredfrequency expressed in kilocycles per second, and the ratio of said Yaxis length dimension with respect to said thickness dimension being oneof the values substantially from 12 to 30, said thickness dimension andsaid dimensional ratio being corresponding values in accordance with thevalue of said frequency.

14. A Rochelle salt type piezoelectric crystal element adapted tovibrate at a desired second shear thickness mode frequency, said crystalelement having substantially rectangular shaped major surfaces, saidmajor surfaces having a length dimension and a thickness or thindimension therebetween, said thickness dimension and said lengthdimension being made of values in accordance with the value of saiddesired second shear frequency, said major surfaces and said lengthdimension being substantially parallel to a Z axis, said major surfacesbeing inclined at an angle of substantially 45 degrees with respect tothe Y axis, said thickness dimension expressed in millimeters being oneof the values substantially from 1060 to 1107 divided by said desiredfrequency expressed in kilocycles per second, and the ratio of said Zaxis length dimension with respect to said thickness dimension being oneof the values substantially from 12 to 30, said thickness dimension andsaid dimensional ratio being corresponding values in accordance with thevalue of said frequency.

WARREN P. MASON.

